What is Countershading?

Countershading also known as Thayer's law is a general concept in biology but also specifically applies in ichthyology and fishing. Countershading can be simply summarized as the coloring of animals with dark on top and light on bottom. Natural shading of objects from the sun does the opposite, hence countering that gives a camouflage effect.

As a general trend for fish, the dark on top along their spine will match what is below them (either the ground or more water) and the bottom typically matches the sky (as viewed from underwater).

So when doing color selection for lures you have two options follow a countershaded color scheme to look more natural or do the opposite to have the lure stand out and be easy to see. The opposite of countershading is also seen in nature, for example, the honeybadger so it's easily seen coloration can serve as a warning.

Ichthyology